This invention pertains to the field of end constraints for torsion bar springs of the solid or laminated type.
Due to the design of presently available end constraints, the magnitude of twist and the load carrying ability of torsion members are substantially limited. One prior art end constraint design for square or rectangular torsion members, features a socket that fits tightly around the end portions of said torsion members. The main disadvantage of this design is that under large torsion member twist, high transverse shear stress prevails within the ends of the torsion member at the transition region between the active and non-active portions, to cause permanent deformation and premature fatigue failure. Also, due to lack of torsion member side clearance within the constraint cavity, the ends of said torsion member will be restrained from curling freely, thereby causing said torsion member to undergo buckling at a distance remote from the trailing faces of said end constraints.
Another design disclosed in U.S. Pat. No. 2,606,020, features an end constraint design having two obliquely opposed support surfaces diverging in the longitudinal direction to form a wedge type cavity that engages the torsion member such as to provide edge contact along its extreme ends. Under large torsion member twist, this design becomes unsuitable because the resulting high edge contact stresses will cause permanent deformation and premature fatigue failure within the overstressed area of the torsion member ends. It should also be noted that as the torsion member is twisted, it shortens in length, thereby causing the ends of the torsion member to move toward the diverging direction with the end constraint cavity. This shortening effect results in a reduction of output load per amount of constraint twist, when compared to end constraints having flat parallel opposing support surfaces.